双调查找：数组先递增后递减

最新推荐文章于 2025-03-17 13:15:15 发布

原创最新推荐文章于 2025-03-17 13:15:15 发布 · 696 阅读

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这篇博客主要介绍了如何在先递增后递减的双调数组中，通过二分搜索算法来查找给定的目标整数。文章详细阐述了检查数组中间元素状态的函数`check`，以及针对不同状态的递归搜索函数`solve`，最后在主函数`main`中进行了测试。这种方法结合了有序数组的特性，提高了查找效率。

双调查找：
如果一个数组中的所有元素是先递增后递减的，则称这个数组为双调的。编写一个程序，给定一个含有N 个不同int 值的双调数组，判断它是否含有给定的整数

#include<iostream>
using namespace std;
#include<vector>

int check(int mid, vector<int>& array) {
	if (array[mid] > array[mid - 1] && array[mid] > array[mid + 1]) {
		return 1;
	}
	else if (array[mid] > array[mid - 1] && array[mid] < array[mid + 1]) {
		return 2;
	}
	else if(array[mid] < array[mid-1]&& array[mid]>array[mid+1]) {
		return 3;
	}
	else {
		return -1;
	}
}

int binarySearchAcend(vector<int>& array, int left, int right, int target) {
	if (left > right) return -1;
	int mid = (left + right) >> 1;
	int res = -1;
	if (array[mid] == target) {
		return mid;
	}
	else if (array[mid] < target) {
		res = binarySearchAcend(array, mid + 1, right, target);
	}
	else {
		res = binarySearchAcend(array, left, mid - 1, target);
	}
	return res;
}

int binarySearchDescend(vector<int>& array, int left, int right, int target) {
	if (left > right) return -1;
	int mid = (left + right) >> 1;
	int res = -1;
	if (array[mid] == target) {
		return mid;
	}
	else if (array[mid] > target) {
		res = binarySearchAcend(array, mid + 1, right, target);
	}
	else {
		res = binarySearchAcend(array, left, mid - 1, target);
	}
	return res;
}

int solve(vector<int>& array, int left, int right, int target) {
	if (left > right) return -1;
	int mid = (left + right) >> 1;
	if (array[mid] == target) return mid;
	int status = check(mid, array);
	if (array[mid] > target) {
		if (status == 1) {
			int res = -1;
			res = binarySearchAcend(array, left, mid - 1, target);
			if (res != -1) return res;
			return binarySearchDescend(array, mid + 1, right, target);
		}
		else if (status == 2) {
			int res = -1;
			res = solve(array, mid + 1, right, target);
			if (res != -1) return res;
			return binarySearchAcend(array, left, mid - 1, target);
		}
		else if (status == 3) {
			int res = -1;
			res = solve(array, left, mid - 1, target);
			if (res != -1) return res;
			return binarySearchDescend(array, mid + 1, right, target);
		}
		else return -1;
	}
	else {
		if (status == 1) {
			return -1;
		}
		else if (status == 2) {
			int res = solve(array, mid + 1, right, target);
			return res;
		}
		else if (status == 3) {
			int res = solve(array, left, mid - 1, target);
			return res;
		}
		else return -1;
	}
	return -1;
}



int main() {
	vector<int> array = { 3,5,6,7,4,2 };
	int target = 7;
	int ans = solve(array, 0, array.size()-1, target);
	cout << ans << endl;
	system("pause");
	return 0;
}